I love Stirling engines! I've designed one out of brass and aluminum. Hopefully someday soon I will actually get around to making it. The one I’ve designed, which will run off of a small candle, won't be anything more than a conversation piece, but it is a great demonstration of how to turn heat into work. I've also learned that if you run the engine in reverse, for example, off of a small dc motor, it will actually create a hot and cold side. Because of this the engines are also used in cryogenics.
